Preparation of piezoelectric resonators



.Fan., 14, 1947. R. H. BRosEKl-:R Erm. 2,414,088

PREPARATION OF PIEZOELECTRIC HESONATORSu Filed oct. '6. 1'29'42'- 2 hnslhliesseaaaer Roland BID-Seher- Parente-d .ha 14,1941

UNITED STATES V 72,414,088 Y. PREPARATION o'F Pmzon nEsoNA'r-oas Roland H. Broseker,

LECTRIC Anne Arundel County,

and James I...l Hessenauer, Baltimore, Md., assignors to Bendix Aviation Corporation, South Bend, Ind., a corporation o! Delaware Appucctionoctober c,

8 Claims.

`This invention relates to the manufacture of piezo-electric resonators and more particularly to an improved method and apparatus for deterng the cutting planes to be used inthe prep eration of 'such resonators. A

It/is vwell known that piezo-electric quart-z elements are excellently suited for the construction of very stable vacuum tube oscillators, and that the Vdegree oflimmu'nlty to frequency variations caused by temperature changes is largelydetermined by the angular` Vrelation between the surfaces of the -resonating element and the axes ci' the mother crystal from which the element is cut. Certain angles must be very carefully control-led during the preparation ofthe crystal rescnator if the desired loW temperature coefllcient is to be realized.' Two of the more popular cuts are: the AT cut in which the major plane surface of the resonator element makes an angle of 35 degrees, 22 minutes with the Z or optical axis; and the BT cut in which the major plane surface of the resonator element makes an angle of 49 degrecs, 47 minutes with the Z axis.v Quartz is termed right or left-handed depending on the direction in which the plane of polarization of plane polarized light is rotated upon traverse of a given sample, and it has been found that the cutting angles must be measured in'one direction from the reference axis for right-handed quartz and in the other direction for left-handed quartz. Initially, these cutting angles were determined by measurements from an intact referenoe face en the mother crystal, by measurements `from the optical .axis as determined by observation under convergent polarized light or by the use of X-rays.

More recently there has beenv described a method of determining the cutting plane to` beused in the preparation of bar stock for crystal blanks in whichV the mother crystal is first cut into slabs employing cutting planes parallel to the Z axis and to the Y or'mechanical axis. These pieces are next etched in hydrouoric acid, washed, dried, and illuminated by the light emanating from a small pinhole and traversing thev piece in a ldirection substantially perpendicular to the optical axis. With a positive electric face adjacent the pinhole, a parallelogram may be seen when the emergent `face of the slab under test is viewed, and it has been found that the direction of the short side of this parallelogram corresponds to that ofV the optical axis, while the long side of the parallelogram is in` clined to this .axis at anV angle of approximately 51 degrees, 46 minutes. The method of deter- 1942, Serial No. 461,015 i (c1. ias- 14) v.. 2`

mining the positions of the cutting planes to be employed in the preparation of bar stock for crystal blanks' having predetermined characteristics, utilizing the sides of the parallelogram as references, is described in a United States patent application iiled August 10, 1942, Serial Number 454,284 by'YR. H. Broseker et al., in which the marking of the quartz slabs withl guide lines established by reference to the sidesy of the above vparallelogram is detailed. While this method of marking represents a considerable advance over the methods which previously found Wide employment, a certain amount o1 mechanical skill and ability to judge the parallelism of the marking straightl edge with the reference side of the parallelogramv is still required. Furthermore, it was necessary to move not only the marking edge but also the quartz slab for each additional guide line required `ior the marking off of a number y of bars on a given slab.

One of the principal objects of this invention is to provide new and novel apparatus for the more rapid and accurate determination of cutting planes in piezo-electric materials.

Another object of the invention is to reduce.v

the amount of labor required for the marking of a plurality of cutting guide lines on Aa slab of crystalline piezo-electric substance.

Still another object of the inventionis to `provide improved apparatus for the establishment o1' cutting lines for piezo-electric crystal blanks in which correct orientation of the work piece is indicated by interlocking patterns.

A further object of `the invention is to proof piezo-electric material may be visually oriented for marking cutting guide lines with improved accuracy and increasedspeem The above objects and advantages o! the invention are' accomplished by locating a properly prepared quartz slab adjacent two illuminated pinholes, observing the light patterns appearing in the emergent face of the slab, orienting` the slab under test so that the adjacent patterns interlock and marking the quartz with a line drawn along one edge of a guide triangle whose base is held in contact with a guiding plane fixed with respect to a line passing through the two illuminated pinholes, guide line is desired, the additional lines may be drawn parallel to the original line by sliding the triangle back and forth along the guiding plane.

Other objects and advantages of the inven- 55 tion will in part be described and in part be vide new and novel apparatus in which a slaby Where more than one.

` the bulb within the box I.

3. obvious when the following specification is read in conjunction with the drawingin which:

Figure 1 is a view of the completed -apparatus inperspective.

Figure 2 is a cut-away side elevation showing the internal construction.

Figures is a top view with the test piece removed showing the work table. i

Figure 4 illustrates the patterns seen with the test piece improperly oriented.

Figure 5 illustrates the patterns seen when the test piece is properly oriented.

in the top view of mure s in which under -test has been removed. Here, the work table 2 with the guide bars 5 and Bllocated along two of the apertures I3 defining two points on a line substantially parallel to. the BT guide 5 and located directly over the light source l0.

parallel to the Y and Zv axes. ','of threeto'four hours in-.a' 48% solution of v lLvdrouori'cl acid and then washed land dried. The light emanating from the pinholes therefore traverses the test slab in. a"directionfperpen.

`Quartz slabs which are tobe marked on thisl apparatusmust beprepared in the proper manner. The slabs are out out-of the mother crystal using cutting planes spaced by about A inch etched'for a period i dicular to the Y and Z ,axes and parallel to the X vectional dissipation of the heat generated by Located along the rear surface of the work table 2 is the guide bar 5 which may be referred to as the'BTguide, while a guide bar 6 is located along one of the short edges of the work table 2 perpendicular to the BT guide and will henceforth be 'referred to as the AT guide. The quartz slab 1 which is to be tested, vis located on the vwork table 2 where it is traversed by the light emanating from two produces patterns in the emergent f ace of the slab 1 which will be more` completely described and discussed in connection with a later. gure. While .observing these patterns, the observer manipulates the slab 1 on the work table until the two patterns interlock and, leaving the slab in this position, a vtriangular shaped marking guide 8 is placed over the quartz slab in the po'sition shown with the extended base 9 thereof maintained in close .contact with the'guidin'g surface of one of the guide bars 5, 6. In Figure 1,the apparatus is--set up preparatory to marking the guide lineson the slab 1 which will indicate fthe cutsto be made for the preparation of bar stock for; the manufacture of BT out blanks.'

or 'electrical axis. mentioned application, each pinhole gives rise -to a parallelogram shaped image in the'emergent face of the slab when that face is at thenegative end of'the X axis, and producesa double ended arrow as an image when the emergent face is at the positive end of the X axis. The apparatus described so .far is intended to -function with the negative face of the crystal slab toward the ob server, that is; with parallelogram shaped images. The images appearing in the emergent face I4 'of the slab 1 are shownin Figures 4 and 5 ior two spacedpinholesin the table 2, and this light When preparing 'AT bar stock, the guide` bar 8 i's used as a reference'.and the triangularshaped markinggulde A is of somewhat different dimensions than thoseemployed in the 'BT triangle. the slab 1 is cut upinto a number of parallel sided bars using ya suitable saw, and the bar stock thus produced is cut up` into crystal- After marking.

line plates or blanks employing a cutting plane normal to the longitudinal axis of the bar. The blanks are then finished to the desired frequency y in the usual manner. 'v

Details ofthe apparatus are more clearly seen in Figure 2, showing the lamp I 0 mounted in the socket II within the box I and connected to the line cord I2 and the on-off switch 3 in series relationship. The work' table 2 is supported on the formed .edgesat the top of the box Ifand is provided with twopinholes or apertures I3 approximately .013 -inch in diameter spaced by. `about inch locatedover the light source lil. Y

The quartz slab 1 is placed on the work table 2 directly over the apertures with the negative end Hof the X- axis up and is rotated by the operator to such a position that'the desired images are visible in the emergent face I4. The position of the pinholes I 3 with to' the guide bars 5 and Bis 'most clearly seen conditions; in Figure 4;',the' patterns I5 indicate that the slab is improperly oriented for the mark ing' operation,while the interlocking images* I5 of Figure 5 illustrate the relationshipv (deserved when the slab 1 has been oriented to the proper position'. In each of these igures, the location of the-pinholey is indicated at I6, and it has been found that each'of the ilgures .15 .rotates about the point I6 as acenterwhen the slab is rotated.

When the gures are ofthe .proper size.' the perfection of interlocking vcan be observed with great accuracy as is clearly seen in Figures 4 and 5. When the figures are interlocked asin Figurel 5, the crystalline'molecular planes parallel to the optical axis within the slab under test make an I v angle of approximately .51 46' -witha line through'fthe centers of the individual gures and consequently with the'line vdeiined by the two apertures, Asthe BT guide 5 is substantially parallel with the line deinedr bythe two apertures, adjustmentofthe slab to cause the igures to interlock places the optical axis at-the predetermined angle of 51 46' to the guide bar 5 and permitsthev use of the triangle V.to inscribe the cutting guide lineson the slab 1. For best results.

it jhasbeen vfound that l'the two .images should overlap only slightlyand as .the sine of theixnage is determined by the-distance'A between the pinholeand the emergent;v face, the slab thickness thereby controlling the'image size, it'has been found that the optimum vseparation of the two pinholes varies with' the thicknessof the slab to be tested. A- pinhole `separation equal to approximately one-half thelthickness oi'` the test slab has yielded vhighlysatisiactory results.

With the slab in such a position that the interlocked nuagesv of Figure 5 are seen, the triangle of Figure (6 igplaced over the top surface of slab 1 with the base ljthereof in contact withithe BT guide Sand a marking pencil drawn along the edge yof triangle lmarked L". The triangle may nowl be `moved laterally a distance equal to the.

. desired width of the bar stock and another line scribed. the' process being repeated until the enf tire slab ismarked of! for cutting into bar stock preparatQry to the'blankcutting. Thus. once the the slab its edges is viewed from the top, showingV As described-in the afore-l sign of the rotatorypolarity.

' -i l5 crystal slab vl has becnorientated to the proper pos'itiomth'e guide lines may be scribed on the adam surface thereof in any desired number without. subsequent movement and the thereby neces.4

sitated Areorientation of the slab. .'.ihis` results in a marked reduction in the time consumed for the performance of the marking operation as only the triangle need -be moved, and its orientation "is always xed by-the Presence of the guide I;

whereas in the former performance of this operation, 'it was necessary -to move the slab and reincident face. orientating said 'slab to cause the light patterns produced in the emergent face of said. slab by said beams to interlock and marking said slab with a line-.making a predetermined anglev with aline determined by two of said ,beama ting-planes inv piezo-electric quartz: source; an opaque plane structural member pro` vided with e plurality of spaced apertures adorientate it each time. Triangle 8,-utilized for the marking .of BT vbar stock. is anl isosceles triangle having an apex angleA of 3 degrees, 58

minutes. The R." and L" markings along the triangle edges indicate the edge to be used as a marking guide for right-handed and left-handed quartz respectively. 'Ihe optical rotatory polarity.

of the quartz slab underitest is readily determined .by inspection oi'y the parallelogram 3.' In apparatus for the determination of cuta light jacent said light source; a guide member having a plane reference surfacasaidguide member be.

ing' so mounted with respect -toV said structural member that said reference surface extends on the side thereof opposite said light source; and a` cuttingplane determining means movable along and in contact with said reference surface, said '1, means having a, straight edge extending across diagrams. The quartz sample is rst rotated so 5 indicates left-handed quartz.

Bar stock for the manufacture of AT cut. crystal blanks is prepared in a. manner similar to that above outlined, except that .the AT. guide 6 is used as a reference and theguide triangle used has .an apen angle of approximately 5'degr'ees, de nduutes.

'lihe L and R are placed along the guide edges of the AT triangle in the same position as shown in Figure 6.

The apparatus described utilizing two spaced pinholes sufdces to illustratethe principle of the invention, and with this in mind, it is seen that a number oi'holes arranged in a straight line or any desiredV geometric pattern may be used to provide more ofthe same kind of images or to indicate correct orientation by a somewhat different nal pattern. A Further, it is clear that.

either the long sides of the/parallelograms or the double-ended arrows produced with the' positive face adiacent the observer may bel employed to indicate orientation if the angle between the line dedned by the apertures and the legs of the l. The method of inscribing cutting guide lines on a slab of piezo-electric quartz having substantially parallel opposite etched principal vfaces parallel to the Y and 'Z axes'which-comprises, pamlng two spaced beams of light through said slab substantially normal to the incident face, orientating said slab to cause the light patterns produced in the emergent facebf said slab by said beams to interlock, and marking said slab with a line making a predetermined angle with the line determined by said beams.

2. The method of inscribing cutting guide lines on a slab of piezo-electric .quartz having substantially parallel opposite etched principal faces parallel to the Y and Z aires which comprises, passing a plurality of spaced beams of light through seid slab substantially. normal to the said plane structural member in a direction along l which the piezo-electric frequency response of a' 'quartz sample will undergo a minimum variation with temperature change, when said sample is in the form of an etched slab with its maior faces parallel to its Y and Z axes and is placed against said plane structural member and said,

apertures, and is of such thickness and` sol orientated that quadrilateral light dispersion patterns formed in said sample by light emerging from said apertures are interlocked by linear fusion. of their' adjacent sides.

Vin In apparatus for the determination oitlng planes in piezo-electric quartz: a lisht source; a light screen provided with two spaced apertures adjacent said light source; and an ele-- nient having a plane guide surface, said element being sov mounted with respect to said light screen that said plane guide surface entends in substantial parallelism with, in facing relation to, and on the same side of said screen as the light beams emanating from said apertures,l whereby; an etched slab of piezo-electric quartz having its major faces parallel to its Y and Z axes and a thickness equal to substantially twice the spacing of said apertures may be placed against said screen and said apertures, and so.

orientated that quadrilateral light dispersion patterns produced therein by said light beams interlock by linear fusion of their adjacent sides. whereupon the lines in said quartz along which piezo-electric frequency response undergoes 'a minimum of variation under changes of tempera,- ture extend in fixed and pre-chosen directions with respect to said 'guide surface; and means movable alongsaid plane guide surface, and 'proj viding an edge extending along one ofsaid directions, forvthe generation of cutting lines on said slab.

5. In apparatus for the determination of cut'- ting planes in piezo-electric quartz: a light source; a substantially plane cpaquelight screen provided with two spaced apertures adjacent said light source, a guide member adjacent said light screen providing a plane reference surface extending beyond the side'of said screen' opposite said light source; and a member mounted for movement along said plane reference surface, the las't named member having edges extending across said light screen and constituting at least portions of the sides of an isosceles triangle based in said plane undergo a minimumv varit'with'temperature change, whensaid sample is inthe form of an cutj such thickness and so 4oxientatedthat quadrilateral light dispersion patterns formed in said sample by light emerging from said apertures are sides 6.vIn apparatus for the determinationA of cutting planes in piezo-electricfquartzz' a 'alight sourcefa substantially plane opaque light screen j, provided with a plurality of spaced apertures adjacent said light source; a fguidemember adjainter-locked by linear fusion of their adjacent reference surface. the

8 last named member having edges extending across said light screen and .constituting at least portions of the sides'ol an -isosceles triangle based in said plane reference surface and having a vertex angle of substantially six degrees.

8. In apparatus for the determination of cutting planes in piezo-electric quartz: a light source; an opaque' light screen provided with two cent said light screen providing a plane refern surface extending beyond the sidefofsaid screen-'oppodte said light source, in substantial beams emerging from 'two of said apertures; and a member mounted for movement along said `plane reference the last named memberlhav ing edges 'extending across said light screen and aimais plane-denned bythe-light spaced apertures adjacent said light source; a

vguide member adjacent said light screen providing a'plane reference surface extending beyond the side of said screen opposite said light source in substantial'parallelism' with the planel denedv vby, the 'light beams emerging from vsaid aper- 'turesia second guide member adjacent said'light screen providing 'a second planereference surface n substantiallyperpendicular to the first mentioned Y referencesurface; and a pair'of cutting-plane constituting at least portions 0i the sides of an isosceles triangle-'based in said plane reference `surface and having a vertex angle of substantial-Il lyfourdeg'rees. v

'l'.'Inapparatusforthe determination of cui:-V

ting planes in piezo-electric quartz: a light f source; Va substantially plane opaque light screen provided with a. plurality of'spaced apertures adv jacent said light source;V a .guide memberadjacentsaidlight screen providing a plane referencev surface extending beyond the side ofsaid screen determiningmeans, each mounted for movement c along a respective one of said reference surfaces, each ofgsaid means .having at least one straight edgeextending across said lightscreen, said edges extending inf directions along which the piezoelectric frequency response of ra quartz sample will undergo a minimum variation with temperaturechangafwhen said sample is in the form of anv etched slab with its major faces parallel to its Y andZ; axes and is placed against said light' screen and said apertures, and is of such thickness and so orientated that quadrilateral light disperopposite said light source in substantial parallel- 'Y ism with the plane dennedrby the light beams V:is

emerging from two of-said apertures; and 'a K member'mounted 'forfmovement along said' plane sion 'patterns formed in said sample by said light fbeamsnare'iinterlocked by linear fusion of their. j adjacent sides.

yROLANI) H. BRSEKER. JAMES A1,. HEssENAUER. 

